Frank Colson on sat 4 jun 05
For those already familiar with using gas for firing kilns, know that liquid
gas, or often referred to as propane and in other parts of the world, as
butane, is simply compressed gas from a natural state. When using and
calculating specs for burners, liquid gas must have smaller orifice
sizes than natural gas. This area of specifications I will leave up to
charts and those in the field who work with these elements on a daily
basis.
I want to make aware some of the zones of precaution and advantage regarding
the two types of gas. First and most importantly, liquid gas is heavier
than air. Often liquid gas is delivered under pressure coming from the main
line (or tank) into the kiln firebox. When using a venturi burner design, a
lot of soot or carbon can accumulate when attempting to "candle" (low
warm-up) a kiln in early stages.
This is rarely the case with natural gas since it is lighter then air and
will disperse into the firebox chamber easily without carbon buildup.
However, liquid gas can be very dangerous if the design of the kiln,
burner(s), or control valves ,are improperly installed.
I would like to illustrate an experience I once had encountered while
teaching at Penland School of Crafts. A co-teacher, not to be named,
brought a new melt furnace with him to replace the one I had made several
years earlier. He had made a beautiful unit which he named: "Big Bertha"
on the outside of the casing. Two modifications he had designed differed
from my model was; a circular opening
in the bottom of the refractory floor ,which stood a few inches above
ground, and a "water valve" attached to the copper line allowing gas to
enter the chamber. The bronze casting area was up a small embankment next
to the glass blowing area. I had just come up from the dinning room with a
cup of coffee in my hand. I entered the open lean-to where my associate
was kneeled down next to
the furnace. His right hand was on the water valve which fed the propane
gas into the combustion chamber. A small soft yellow flame was licking out
of the top of the furnace opening. I turned my head away for a split
second, heard a loud "PoP", turned back , to witnessed a running figure on
fire. Every inch of my associate's body was in full flame! Actually! A
human fireball! Fortunately, the flame consumed
itself quickly and left him looking like toasted sunburn with a look of
astonished disbelief.
The moral of this real life example is that heavier than air gas can be
very scary! The first mistake in this incident,
was installing a water valve on a gas line. That's strictly a NO NO! It
takes many turns of the handle to allow fuel flow. A gas petcock valve does
the job properly and quickly. The 2nd mistake was having a hole in the
bottom of the furnace, which allowed
uncombusted gas to seep and pool on the ground outside the furnace where my
associate was cranking the water valve open. In seconds, that lazy flame
above, arched out over the top of the furnace and ignited the accumulated
fuel pooled several feet around the ground.
In a less dramatic fashion I have witnessed related happenings when lighting
burners on a kilns. Who needed those eyebrows, anyway? Even so, natural
gas can also cause a traumatic result if a kiln designed is modified.
Such was the case of a large 20 cu. ft. natural gas updraft kiln I had
built for a ceramic league once, which blew out the door and knocked the
operator flat on her back. But THAT is another story!
Frank Colson
www.R2D2u.com
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